The Department of Homeland Security (DHS) believes the series of distributed denial of service (DDoS) attacks that disrupted major websites across the US East Coast on Friday have been mitigated. The attacks targeted Dyn, a New Hampshire-based Internet performance management company. A DDoS attack is an attempt to make an online service unavailable by overwhelming the targeted system with data. Users reported on Friday they had trouble accessing a number of popular websites, such as Twitter, Reddit, and Spotify. Kyle York, chief strategy officer for Dyn, said the attacks came in three waves, first hitting the East Coast and later spreading westward. DHS Says Massive DDoS Attack Against Dyn Has Been Mitigated